For many patients with severe heart, kidney, and other diseases, transplantation is the only option for treatment. However, although elderly represent a growing population with end-stage organ disease, these older patients have worse outcomes including increased likelihood of death and increased rates of infections after transplantation as compared with younger patients. Studies into the biology of elderly patients has revealed evidence of T cell dysfunction in elderly patients where these cells, which play a central role in the defense against infections, begin to display markers of exhaustion and aging. Other studies have suggested that the response against a common human virus which causes chronic infection in healthy adults, cytomegalovirus, is also associated with the biological aging of the immune system. We propose for the first time, to assess for evidence of these changes in the elderly transplant recipient, focusing on kidney transplant recipients because of the large numbers of these patients transplanted at our center. To follow up on these studies we will analyze the pattern of gene expression that is associated with T cell dysfunction in these patients. Finally, we use bioinformatics techniques to evaluate the large amounts of data generated as described above and to look for patterns most strongly associated with the elderly transplant recipient to enable us to design a noninvasive test for monitoring immune function in patients before and after transplantation. This type of testing ability would allow for customization of immunosuppression medication regimens after transplantation, allowing elderly patients with end stage organ disease to benefit from transplantation with less risk of infectious complications.